1. Field of the Invention
The present invention relates to an optical waveguide for a touch panel.
2. Description of the Related Art
Touch panels are input devices for operating an apparatus by directly touching a display screen of a liquid crystal display device or the like by a finger, a special stylus or the like, and include a display which displays operation items, and detection means which detects the position (coordinates) of a portion of the display screen of the display touched by the finger or the like. Information of the touch position detected by the detection means is sent in the form of a signal to the apparatus, which in turn performs an operation specified by the touch position. Examples of the apparatus employing such a touch panel include ATMs in banking facilities, ticket venders in stations and portable game machines.
A detection device employing a light transmission device is proposed as the detection means for detecting the finger touch position on the touch panel (see, for example, U.S. 2004/0201579A1: Patent Document 1). That is, the light transmission device includes an optical waveguide which is disposed along a periphery of a display screen of a rectangular display and is configured such that a multiplicity of light beams are emitted parallel to the display screen of the display from an optical waveguide portion disposed on one side of the display screen of the display and incident on an optical waveguide portion disposed on the other side. The light transmission device causes the light beams to travel in a lattice form on the display screen of the display. When a portion of the display screen of the display is touched by a finger in this state, the finger blocks some of the light beams. Therefore, the position of the portion touched by the finger is detected by detecting a light blocked portion by the optical waveguide portion on the light incident side.
On the other hand, a light transmission device having a higher light transmission efficiency is also proposed (see, for example, JP-A1-2003-4960: Patent Document 2). In an ordinary optical waveguide, light emitting faces (end faces of cores) are flat, so that light beams emitted from the optical waveguide are radially diverged in air. Therefore, the light transmission efficiency is reduced. In the light transmission device of Patent Document 2, on the contrary, a light emitting optical waveguide has a first lens provided at an end thereof as having the same three-layer structure as the optical waveguide including an under-cladding layer, a core layer and an over-cladding layer. The first lens prevents lateral divergence of a light beam. Further, a second lens is disposed in front of the first lens (downstream of the first lens in a light traveling direction) apart from the first lens. The second lens prevents vertical divergence of the light beam. Thus, the light beam having passed through the second lens is collimated. Further, a light incident optical waveguide also has first and second lenses, so that the collimated light beam is vertically converged by the second lens and laterally converged by the first lens. Thus, the converged light beam is incident on the light incident optical waveguide. This increases the light transmission efficiency.
In the light transmission device of Patent Document 2, however, the first lenses and the second lenses are provided as separate members. Therefore, unless the lenses are accurately positioned, it is impossible to sufficiently increase the light transmission efficiency. In addition, the positioning of the lenses is time-consuming.